This paper presents a simpler method to predict the C - J state of high explosive based only on
the initial density dependence of detonation velocity. To predictC - J pressure by this method,
for example, we need the slope of the detonation velocity as a function of initial density.
We first define a succession of C - J states on a pressure - volume - energy state surface. Available
data set of the initial density dependence of the detonation velocity gives a collection of Rayleigh
lines. The C - J state curve can be approximated by an envelope function of Rayleigh lines. This
envelope function can be given by a simple mathematical function. Present approximation
gaves an exccelent description of the C - J state curve especially on p - v plane. Since the detonation
velocity is a sensitive function of initial density, and the measurements can be made very
accurately. this method may serve a handy and relatively easier method to estimate the C - J
state for high explosive. The physical meanings of the approximation is discussed in
thermodynamic terms, which revealed that it is the approximation that the Grüneisen parameter
is set to zero.